<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>3-02 半透明填充fill-opacity</title>
</head>
<body>
  <svg width="400" height="400">
    <rect
      width="200"
      height="100"
      fill="red"
      fill-opacity="0.2"
    />
  </svg>
</body>
</html>